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Cracked Threads on Cam Guide

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Hi All, 

First time posting here, just reaching out for information on what can be done about this situation. In course of replacing a valve cover gasket several years ago, I noticed a tiny crack in the threads for one of the valve cover mounts on the exhaust cam guide. I believe it's from the previous owner over tightening it. Well, my bike was leaking oil all over the side of the head so I took the cover off again the other day, before a ride, to apply some silicon and take care of that oil leak. In doing so I noticed the crack has gotten considerably worse. Here is a picture: 

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In looking at it, it appears that even if it cracked all the way, nothing would really happen, as the cam itself is held in place on either end by the 4 bolts, and the "bridge" in the middle mostly serves as a location for those threads to hold the cover on. It also is my understanding that this guide is machined with the head (or something like that), so you can't just get another exhaust cam guide and bolt it on. But, this hasn't ever really made sense to me as I have hot cams in my bike as well installed by previous owner, and those have a different profile than stock cams but don't require any machining, just drop and go. Bike currently runs like a top. So, what are my options? I saw a few other, older posts where something similar happened. It seems perhaps having a shop plug weld it then drill new hole would be the preferred approach but not sure.

Much appreciated.

-Brad 

Edited by Bilbo Swaggins

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If I saw that in my bike I'd be looking to replace the cam cap asap . As simple as they are they hold a pretty  important role . If its a Budget job you can probably snag a Cam Cap off Ebay and have it fitted properly or  find a deal that has Cam and cap matched and might get by with a bolt on and go scenario .

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Yep replace it - if that let go it could cost you 4 times as much

Camshaft holders are separate if you can find one

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I'm going against the grain here...I say weld it!  I actually welded one on my crf250 and it worked out just fine... (going on 4 yrs. now)

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There are competent shops (like Engine Dynamics) that can weld that and make it as good as new without affecting the journal. They may or may not want to go a step further and install a Time-Sert. When tightening those bolts, once the shoulder of the bolt bottoms on the cam cap, just a tiny snug more is all that is needed. There is no bolt tension/clamping force used.

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The exhaust caps are usually the ones that break . When I bought a cheap pooched head it had the cap broken as well , it was hard to locate an exhaust cap , plenty of intakes though . I shaved a couple thousanths off both mating surfaces and rebored the cam bore , worked good . Our welders didn't like the oil contaminated cast aluminum as a reliable fix plus no idea what alloy it was so I didn't even try , either way I had to bore the journals to get rid of some smearing from lack of oil .

 

.

Edited by jjktmrider
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Thanks for the replies everyone. I'm definitely going to fix it...just need to decide on the best course of action. I talked to my buddies dad, who is a master mechanic, and he mentioned a few of the same things. One suggestion he had was to install a time-sert with epoxy rather than weld it, because a) as jjktmrider mentioned, the metal is contaminated with oil which the welders may have trouble with and b ) welding it could cause the metal to warp and affect the profile/ position of the journal surface. What's the consensus on a good epoxy? 

Also, let's say I somehow obtain a used exhaust cam cap without buying a whole new head. Where can I take it to have it machined properly to match my head? I live in socal so I was thinking perhaps pro circuit or yoshimura which are local to me. 

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probably any competent machine shop could fit a new cap, thats probably what i would do 'but' the head is going to have to come off and i would wait until it was off sometime to do it ... for the time being my approach would be to spray that hole out good with brake cleaner, run the screw in with blue loctite and let it eat ..

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12 hours ago, jjktmrider said:

 I had to bore the journals to get rid of some smearing from lack of oil .

Pics? :)

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30 minutes ago, jjktmrider said:

the "new" cap and how it fit before doing anything , 

DSCN1440_zpsw7z5qnlq.jpg

 

 

DSCN1451_zpse8esaalp.jpg

Ah ok. I can see why they need to be machined together now. Because the journal is fine on my bike, it's just the "bridge" between them holding the cover threads that's cracked, what's the consensus on simply applying a good metal epoxy to the crack the avoid it spreading? Bolt still threads in ok, it's not currently leaking oil. I messaged engine dynamics and they will re bore if I find a new cap for $175 (plus I gotta ship it there and back). Only cap I found was on eBay for an ltz400 and it was $100 so altogether still a bit expensive. 

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Ah ok. I can see why they need to be machined together now. Because the journal is fine on my bike, it's just the "bridge" between them holding the cover threads that's cracked, what's the consensus on simply applying a good metal epoxy to the crack the avoid it spreading? Bolt still threads in ok, it's not currently leaking oil. I messaged engine dynamics and they will re bore if I find a new cap for $175 (plus I gotta ship it there and back). Only cap I found was on eBay for an ltz400 and it was $100 so altogether still a bit expensive. 

Epoxy is for home project, not metal repairs. A competent tig welder should be able to repair yours without warping.
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Once cracked you loose the stability and strength in the whole cap . With only 2 bolts holding there isn't much strength holding it forward and back even with the 2 halves glued together . I'd never trust any epoxy or jb weld in something like that . Welding would be much better for less likely to break again . As long as when it's welded they bolt the 2 halves down , I'd drill and tap a plate along with the 2 locating dowels to hold the cap tight when welding and leave it there until fully cooled down . That'll give the best chance of not warping but I can guarantee the 2 halves will not be perfectly inline as they were before cracked , just no way to get them back together like that , but very possible they'll be good enough or at least fairly good and usable. If the welder just holds the 2 halves together and tacs them , then welds with it loose , it'll be crap and that welder is one of those that fine tunes everything with a 5lb hammer and claims "perfect".

I had to repair the journal on my head anyways because it was smeared and since I machine my own stuff there was no cost . I got my cap from an LTZ as well because it was half price as the one or 2 from a DRZ , ebay sellers tend to charge more for some reason . Unfortunately all these caps sold individually screw over the seller for the head itself , most people in the know don't buy them without the matching caps . So many sellers are so stupid and/or greedy pricks trying to sell each bolt separate so I hope they gets screwed then and can't sell the head.

 

.

Edited by jjktmrider
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UPDATE

There's a fabricator I know through my Dad who says he can weld it for me no problem, so I'm going to go with that route. Will try and follow through with this post with everything until it's fixed so that other's down the line can benefit from either my success or failure in doing this. Today I took the cap off and cleaned it best I could. My process was:

1. Wipe oil off with rag

2. Soak in Simple Green concentration and let sit

3. Diluted simple green and scrub brush cleaning

4. Sit in cup of gasoline for a few minutes

5. Wash in sink with lots of soap and scrub brush

6. Rinse then soak in near boiling water. Water stayed perfectly clear

7. Let dry in sun for a few minutes

Slight scoring of surface underneath but generally looks ok? Bonus pic of bike too. 

 

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Edited by Bilbo Swaggins

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